Supply of electricity from providers such as power stations, to consumers, such as domestic households and businesses, typically takes place via an electricity distribution network. FIG. 1 shows an exemplary distribution network comprising a transmission grid 100 and a distribution grid 102. The transmission grid is connected to generating plants 104, which may be nuclear plants or gas-fired plants, for example, from which it transmits large quantities of electrical energy at very high voltages (in the UK, for example, this is typically of the order of 204 kV; however this varies by country), using power lines such as overhead power lines, to the distribution grid 102; although, for conciseness, only one distribution grid 102 is shown here, in practice a typical transmission grid supplies power to multiple distribution grids. The transmission grid 100 is linked to the distribution grid 102 via a transformer node 106, which includes a transformer 106 which converts the electric supply to a lower voltage (in the UK, for example, this is typically of the order of 50 kV; however, this varies by country) for distribution in the distribution grid 102. The distribution grid in turn links, via substations 108 comprising further transformers for converting to still lower voltages, to local networks such as a city network 112 supplying domestic users 114, and to industrial consumers such as a factory 110. Smaller power providers such as wind farms 116 may also be connected to the distribution grid 116, and provide power thereto.
The total power consumption associated with a given network varies considerably from time to time; for example, peak consumption periods may occur during the hottest part of the day during summer, when many consumers use their air conditioning units. Since it is expensive to store electricity in large quantities, it is usually generated when it is required, which can place a burden on providers as they attempt to meet demand at peak times.
In recent years, there has been an increased demand for more efficient ways of managing power distribution in electricity networks; in particular it is desired to reduce wasteful electricity consumption in order to reduce costs and the adverse effect that some methods of electricity generation have on the environment. There is also a shift towards forms of power generation, such as wind power and solar power, which may only be able to supply power intermittently when conditions allow, increasing the need to reduce variation in power consumption with time. Furthermore, there is also a trend towards more distributed forms of power provision. For example, individual households and businesses are increasingly generating their own power, for example using solar panels installed on their premises; surplus power generated using these power sources may be sold back to the provider managing the network to which it is connected. Personal Electric Vehicles (PEV) are a further example of an electricity provider; PEVs typically have the capacity to store a large amount of electricity, and may be connected to an electricity network when they are stationary; this means that, in addition to being consumers of power, they can be used as a source of power for the network at times of high demand, with electricity stored in the battery of the PEV being fed back to the network at such times.
In order to meet these changing requirements, more sophisticated methods of measuring and controlling power consumption are desirable. More sophisticated networks, sometimes known as “smart grids”, have been proposed, which may include may include features such as a capability to turn off certain household appliances or factory processes at times of peak demand. These smart grids may use sophisticated meters, sometimes known as “smart meters” capable of intermittently measuring power consumption in near real time, and of indicating energy prices to consumers; this information may be read manually, or it may be transmitted automatically over a communications network using, for example, TCP/IP technology, to a central location.
However such meters are typically located at the premises of a consumer or provider, and measure the amount of electrical power flow as a total of all devices located in the premises. This means that power flows relating to individual devices at a given premises, or a group of devices distributed across multiple premises, cannot easily be measured, particularly in view of the relatively high cost of smart meters making it prohibitive to install a separate meter at each power consuming and/or providing unit to be measured.
It is an object of the present invention to at least mitigate some of the problems of the prior art.